Evaporable getter devices for mounting in electron tubes are well known in the art.
See for example UK Patent No. 898,505 and U.S. Pat. Nos. 3,023,883; 3,211,280 and 3,920,355. These getter devices have a U-shaped cross section and generally yield a quantity of getter material frequently barium, which is less than about 100 mg. With the introduction of larger sized electron devices or television picture tubes it has been found necessary to increase the quantity of getter material evaporated from a getter device. Getter devices capable of releasing larger quantities of getter material have been described for instance in U.S. Pat. Nos. 3,428,168; 3,457,448 and 4,642,516. These getter devices can release from about 125 mg to 230 mg of getter material. They employ the concept of a U-shaped channel container which however has a relatively large channel width. The use of such wide channels has lead to the necessity of preventing detachment of the getter metal vapour releasing material from the channel as is dramatically shown in U.S. Pat. No. 3,457,448 FIGS. 6 and 7. The above three patents try to overcome such disadvantages in these U-shaped cross-section getter devices.
Even larger sized tubes require even greater quantities of getter material. Attempts to provide such large quantities of getter materials such as 400 mg or more have been described in U.S. Pat. Nos. 3,558,962 and 3,560,788. See also FIGS. 9 and 10 of U.S. Pat. No. 3,385,420.
While pan-shaped getters such as those described in U.S. Pat. Nos. 3,558,962 and 3,560,788, mentioned above, have proved capable of giving yields of up to about 400 mg of barium with a release of about 80 to 85% of the barium content, they present certain disadvantages.
U.S. Pat. No. 3,558,962 described a pan-shaped getter in which is inserted a screen which acts as a reinforcing means to hold the getter residue in the container after flash. The screen is also said to conduct heat into the central mass of getter material. Unfortunately the addition of this screen causes a substantial increase in the total mass of the getter device comporting the known disadvantages inherent therein. In addition the screen structure forms closed electrical circuits in the external periphery of the getter device such that when the radio frequency induction heating is applied, overheating takes place in localized areas which can provoke melting of the getter container walls.
An alternative structure of a pan-shaped getter device has been described in U.S. Pat. No. 3,560,788 which however presents the same inconveniences. Furthermore the external wall is fabricated separately from the bottom wall. This leads to additional manufacturing expenses in attaching the two components together, and furthermore it is necessary to add yet another component in the form of a disc adjacent to the separate bottom wall.
If the intensity of the RF induced currents are reduced to try to avoid the melting problem then it is found that a long time elapses before the getter metal starts to evaporate (start time) and excessively long times are required to ensure evaporation of a sufficient quantity of getter metal (total time).
Furthermore the getter devices described in both U.S. Pat. Nos. 3,558,962 and 3,560,788 refer to getter devices having an outer wall diameter of 25 mm. When it is necessary to use a getter device with a smaller outer diameter and having the same high yield of getter material the above mentioned disadvantages remain.